Ion implantation is a process for introducing of introducing dopants, additives, or impurities into a substrate via ion bombardment. Known ion implantation systems or apparatus may comprise an ion source and a series of beam-line components. The ion source may comprise a chamber where desired ions are generated. The ion source may also comprise a power source and an extraction electrode assembly disposed near the chamber. The beam-line components, may include, for example, a mass analyzer, a first acceleration or deceleration stage, a collimator, and a second acceleration or deceleration stage. The ion beam passes through the beam-line components and may be directed toward a substrate mounted on a platen or clamp. The substrate may be moved in one or more dimensions (e.g., translate, rotate, and tilt) by an apparatus, sometimes referred to as a roplat.
In many applications, semiconductor substrates to be implanted have a bulk resistivity in the range of 10-30 Ω-cm, while in certain applications so called high bulk resistivity (HBR) substrates may be employed, where bulk resistivity exceeds 10-30 Ω-cm. Such resistivity values may be found, for example, in substrates for use in so called radio frequency silicon-on-insulator (RF SOI) devices or sensor devices.
One issue encountered when implanting HBR substrates such as semiconductor wafers having resistivity above 10-30 Ω-cm is the ability to process the HBR semiconductor wafers (“HBR wafers”) without encountering handling errors during an implantation process, including processing in high current or medium current ion implantation apparatus. For example, electrostatic clamps may be used as wafer holders, where a clamp current is monitored during implantation for the purposes of detecting the presence or absence of a wafer on the electrostatic clamp. The monitoring of clamp current may insure wafer security to avoid wafer slippage and the risk of dropping a wafer during an implantation process. This method may work adequately for substrates having a resistivity of 10-30 Ω-cm, but may not work well for HBR substrates, leading to wafer handling problems.
For example, in some ion implantation systems, a safety mechanism may be employed, where an ion implanter stops implanting a wafer when the wafer clamp current becomes unstable, such as when large variations are detected. Because HBR wafers may engender such instabilities, the processing of HBR wafers in an ion implanter may be compromised, such as causing unnecessary shutdowns of an ion implanter when clamp current fluctuations become excessive. Many variables may complicate the ability to maintain stable monitoring of HBR wafers including the deviation of bulk resistivity from the reported value from the wafer supplier, variation in HBR wafer characteristics during implantation, such as causing intermittent, rapid reduction in clamp current with sequential implantation, as well as changes in bulk resistivity following implant.
With respect to these and other considerations the present disclosure is provided.